In over-the-horizon radar (OTHR) systems, the signal-to-clutter ratio (SCR) used for
moving target detection is very low. For slowly moving targets such as ships, the SCR is typically
from 250 dB to 260 dB and their Doppler frequencies are close to that of the clutter. For
manoeuvring targets, such as aircraft and missiles, the Doppler frequencies are time-varying when a
long integration time is considered. When a target does not move uniformly, the Fourier transform
based target detection techniques, including super-resolution spectrum techniques, may fail to work
appropriately. In such situations, the Doppler signatures are time-varying and, therefore, time–
frequency analysis techniques can be used for manoeuvring target detection. In addition, clutter
rejection is also required for target detection due to the low SCR. The existing adaptive clutter
rejection algorithms combine clutter rejection with spectrum analysis methods, which usually
assume uniformly moving target (i.e. sinusoidal Doppler signature) models. An adaptive clutter
reject algorithm is proposed together with the adaptive chirplet transform technique for
manoeuvring target detection in a multipath environment. Simulation results using a simulated
manoeuvring target signal with received raw OTHR clutter data show that targets with SCR below
250 dB can be detected by using the proposed algorithm.